Carbon fibers are well known by their applications to technical use; in particular, they find numerous uses in composite materials.
There are two types of carbon on the market, sold as continuous multifilaments in the following counts:
______________________________________ Number of filaments Metric number ______________________________________ 3K (K = 10.sup.3) 5.12 6K 2.56 12K 1.28 40K 0.38 ______________________________________
These two types of carbon are differentiated by their physical properties:
______________________________________ (HM) High Strength (HS) High Modulus ______________________________________ Carbon content 97% 99.5% Strength 3.3 GPa 2.2 GPa Young's modulus 230 GPa 335 GPa Breaking 1.55% 0.75% elongation Density 1.78 1.86 Diameter of fibers 6.8 microns 6.6 microns ______________________________________
The variety of counts proposed by the producers therefore is very limited.
Moreover, the filaments are in the form of very smooth flat ribbons which pose problems with regard to stability of nets made from these fibers, in particular in the case where the product is woven.
At present there are no carbon fiber yarns on the market which meet the needs of many different sectors, and particularly which have a wide range of fine counts which do not exist in multifilaments.
Actually, the only cut carbon fibers which are now encountered comprise fibers of very small dimensions, which are obtained by mechanical cutting with a knife and which in no case are able to be joined to constitute fiber yarns.